Signal processing method and apparatus

ABSTRACT

A signal processing apparatus includes an input voltage selector configured to select an input voltage from a plurality of input voltages; an input element connected to the input voltage selector; and an input current controller configured to control an inflow of an input current in conjunction with an operation of the input voltage selector.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit under 35 USC 119(a) of Korean PatentApplication Nos. 10-2014-0060542 filed on May 20, 2014, and10-2015-0017881 filed on Feb. 5, 2015, in the Korean IntellectualProperty Office, the entire disclosures of which are incorporated hereinby reference for all purposes.

BACKGROUND

1. Field

The following description relates to signal processing technology forprocessing an input signal and generating an output signal.

2. Description of Related Art

An instrumentation amplifier (IA) is used to measure various signals.For example, in a medical field, the IA may be used to measure andamplify a biosignal such as an electrocardiogram (ECG), anelectromyogram (EMG), a photoplethysmogram (PPG), a bioimpedance, amovement signal, or any other biosignal.

In general, the IA may be implemented using a differential amplifierhaving a low offset, low noise, a high common-mode rejection, a highloop gain, and a high input resistance. The IA may include a choppercircuit to modulate a measured signal into a signal of a high-frequencyband or demodulate the modulated signal into a signal of a low-frequencyband.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In one general aspect, a signal processing apparatus includes an inputvoltage selector configured to select an input voltage from a pluralityof input voltages; an input element connected to the input voltageselector; and an input current controller configured to control aninflow of an input current in conjunction with an operation of the inputvoltage selector.

The signal processing apparatus may be configured to be operable in avoltage measuring mode and a current measuring mode.

The input voltage selector may be configured to apply a preset referencevoltage to the input element in the current measuring mode, and apply aninput voltage to be measured to the input element in the voltagemeasuring mode.

The preset reference voltage may have a fixed voltage level or avariable voltage level.

The input current controller may be configured to allow the inflow ofthe input current into the signal processing apparatus in the currentmeasuring mode, and block the inflow of the input current in the voltagemeasuring mode.

The input element may be configured to generate a current in response tothe selected input voltage in the voltage measuring mode.

The input current controller may include an input current compensatorconfigured to output a compensation current to adjust a level of theinput current in the current measuring mode.

The apparatus may further include an input current compensationcontroller configured to control a level of the compensation currentoutput by the input current compensator based on an output signal of thesignal processing apparatus.

The apparatus may further include a low-pass filter configured toextract a signal of a low-frequency band from an output signal of thesignal processing apparatus and output the signal of the low-frequencyband; a comparator configured to compare a level of the signal output bythe low-pass filter to a level of a preset reference signal and output asignal indicating a result of the comparing; and an input currentcompensation controller configured to generate a control signal tocontrol the input current compensator based on the signal output by thecomparator.

The input current controller may include a chopper configured tomodulate a frequency component of the input current based on a controlsignal in the current measuring mode.

The may further include a load element functionally connected to theinput element and the input current controller.

An output end of the input current controller may be connected to bothends of the load element, and one end of the input element may beconnected to one of the ends of the load element.

In another general aspect, a signal processing apparatus includes avoltage input circuit configured to receive an input voltage; a currentinput circuit configured to receive an input current; an amplifierconfigured to amplify one of the input voltage and the input current ata time; and a controller configured to control a connection between thevoltage input circuit and the amplifier, and control a connectionbetween the current input circuit and the amplifier.

The controller may be further configured to block the connection betweenthe current input circuit and the amplifier and connect the voltageinput circuit to the amplifier in a voltage measuring mode.

The controller may be further configured to block the connection betweenthe voltage input circuit and the amplifier and connect the currentinput circuit to the amplifier in a current measuring mode.

The current input circuit may be further configured to adjust a level ofthe input current in response to the level of the input current beinggreater than a preset value and output the input current having theadjusted level in a current measuring mode.

The input voltage may be an electrocardiogram (ECG) signal, and theinput current may be a photoplethysmogram (PPG) signal.

In another general aspect, a signal processing apparatus includes alight source unit configured to output a light signal to a body of auser; a light detector configured to detect a first biosignal measuredbased on the light signal; a bioelectrode configured to detect a secondbiosignal measured based on a voltage signal; a signal processorconfigured to amplify the first biosignal or the second biosignal basedon a measurement mode; and a controller configured to control themeasurement mode of the signal processor.

The signal processor may be further configured to be operable in acurrent measuring mode and a voltage measuring mode; and the controllermay be further configured to control the signal processor to amplify thefirst biosignal in the current measuring mode, and control the signalprocessor to amplify the second biosignal in the voltage measuring mode.

The first biosignal may be a photoplethysmogram (PPG) signal, and thesecond biosignal may be an electrocardiogram (ECG) signal.

The light source unit may include a plurality of light sources; and thecontroller may be further configured to sequentially activate at leastone light source among the light sources during each of a plurality oftime intervals, and determine a light source for measuring the firstbiosignal from the light sources based on a level of a signal outputfrom the light detector during each of the time intervals.

In another general aspect, a signal processing method includes selectinga voltage measuring mode or a current measuring mode; and controlling atype of an input voltage selected and an inflow of an input currentbased on a result of the selecting.

The controlling may include blocking the inflow of the input current andselecting a voltage to be measured as the input voltage in response tothe voltage measuring mode being selected.

The controlling may include selecting a preset reference voltage as theinput voltage and allowing the inflow of the input current in responseto the current measuring mode being selected.

The controlling may include adjusting a level of the input current to bewithin a preset range.

In another general aspect, a non-transitory computer-readable storagemedium stores instructions to cause a computer to perform the methoddescribed above.

In another general aspect, a signal processing apparatus includes anamplifier configured to receive a plurality of input voltages and aninput current and including an amplifying circuit configured to amplifyboth a voltage and a current; and a controller configured to control theamplifier to amplify a selected one of the input voltages and the inputcurrent using the amplifying circuit.

The input voltages may include a voltage to be measured and a referencevoltage; and the controller may be further configured to control theamplifier to block the input current from being applied to theamplifying circuit and apply the voltage to be measured to theamplifying circuit to measure the voltage to be measured in a voltagemeasuring mode, and apply the reference voltage and the input current tothe amplifying circuit to measure the input current in a currentmeasuring mode.

The amplifier may include a first chopper configured to selectivelymodulate the input current; the signal processing apparatus may furtherinclude a second chopper configured to selectively modulate the voltageto be measured, and a third chopper configured to selectively demodulatean output signal of the amplifier; and the controller may be furtherconfigured to control the first chopper to block the input current frombeing applied to the amplifying circuit in the voltage measuring mode,and apply the input current to the amplifying circuit in the currentmeasuring mode.

The amplifying circuit may include a transconductance amplifierconfigured to output a current obtained by amplifying the selected oneof the input voltages and the input current; and the signal processingapparatus may further include a transimpedance amplifier configured toamplify the output current of the transconductance amplifier and outputa voltage obtained by amplifying the output current.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of an overall operationperformed by a signal processing apparatus.

FIGS. 2 and 3 are diagrams illustrating an example of a circuit forimplementing a signal processing apparatus.

FIG. 4 is a diagram illustrating another example of a circuit forimplementing a signal processing apparatus.

FIG. 5 is a diagram illustrating an example of a signal processingapparatus operating in a voltage measuring mode.

FIGS. 6A and 6B are diagrams illustrating examples of operating an inputchopper based on a control signal.

FIGS. 7A through 7C are diagrams illustrating examples of a controlsignal input for each chopper in a voltage measuring mode.

FIGS. 8 and 9 are diagrams illustrating examples of a signal processingapparatus operating in a current measuring mode.

FIGS. 10A through 11C are diagrams illustrating examples of a controlsignal input for each chopper in a current measuring mode.

FIG. 12 is a diagram illustrating an example of an operation performedby a signal processing apparatus in an automatic adjustment mode foradjusting an input current level.

FIG. 13 is a diagram illustrating an example of a configuration of atransimpedance stage.

FIG. 14 is a flowchart illustrating an example of a signal processingmethod.

FIGS. 15 through 16B are diagrams illustrating examples of a wearabledevice including a signal processing apparatus.

FIG. 17 is a diagram illustrating an example of an optical sensor.

FIG. 18 is a diagram illustrating an example of a signal processingapparatus.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements. The drawings may not be to scale,and the relative size, proportions, and depiction of elements in thedrawings may be exaggerated for clarity, illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein will be apparent to one of ordinary skill inthe art. The sequences of operations described herein are merelyexamples, and are not limited to those set forth herein, but may bechanged as will be apparent to one of ordinary skill in the art, withthe exception of operations necessarily occurring in a certain order.Also, descriptions of functions and constructions that are well known toone of ordinary skill in the art may be omitted for increased clarityand conciseness.

The features described herein may be embodied in different forms, andare not to be construed as being limited to the examples describedherein. Rather, the examples described herein have been provided so thatthis disclosure will be thorough and complete, and will convey the fullscope of the disclosure to one of ordinary skill in the art.

FIG. 1 is a diagram illustrating an example of an overall operationperformed by a signal processing apparatus 100.

The signal processing apparatus 100 measures a current or a voltage foreach channel in a multichannel environment. The signal processingapparatus 100 may operate in a voltage measuring mode, a currentmeasuring mode, and a combination mode. The combination mode is ameasurement mode that changes between the voltage measuring mode and thecurrent measuring mode in response to a control signal. The signalprocessing apparatus 100 measures an input voltage and an input currentusing a single integral circuit configuration. The signal processingapparatus 100 provides compatibility between a voltage measurement and acurrent measurement by controlling processing of the input voltage andthe input current input to a measurement circuit based on a controlsignal.

In one example, the signal processing apparatus 100 is included in aninstrumentation amplifier (IA), and the IA uses the signal processingapparatus 100 to selectively measure the voltage and the current. Forexample, the IA including the signal processing apparatus 100 mayamplify a voltage measurement-based biosignal such as anelectrocardiogram (ECG), or a current measurement-based biosignal suchas a photoplethysmogram (PPG). The signal processing apparatus 100measures the ECG in the voltage measuring mode, and measures the PPG inthe current measuring mode.

Referring to FIG. 1, the signal processing apparatus 100 includes acurrent input circuit 110, a voltage input circuit 120, a controller130, and an amplifier 140.

The voltage input circuit 120 receives an input voltage. The inputvoltage may be, for example, an ECG signal measured from a body of auser. The current input circuit 110 receives an input current. As anexample, the input current may be a biosignal including a blood oxygensaturation level, for example, peripheral capillary oxygen saturation(SpO₂), or a PPG signal measured from the body of the user.

The amplifier 140 amplifies either the input voltage or the inputcurrent under a control of the controller 130. The amplifier 140amplifies the input voltage output from the voltage input circuit 120 orthe input current output from the current input circuit 110 based on ameasurement mode. The measurement mode is selected from the voltagemeasuring mode for measuring the input voltage and the current measuringmode for measuring the input current.

The controller 130 controls a connection between the voltage inputcircuit 120 and the amplifier 140 and a connection between the currentinput circuit 110 and the amplifier 140. For example, the controller 130performs a switching operation to select a signal to be applied to theamplifier 140 from the input current and the input voltage. In thevoltage measuring mode, the controller 130 blocks the connection betweenthe current input circuit 110 and the amplifier 140, and connects thevoltage input circuit 120 to the amplifier 140. Accordingly, the inputcurrent received by the current input circuit 110 is not input to theamplifier 140, and the input voltage output from the voltage inputcircuit 120 is input to the amplifier 140 to be amplified.

In the current measuring mode, the controller 130 blocks the connectionbetween the voltage input circuit 120 and the amplifier 140, andconnects the current input circuit 110 to the amplifier 140.Accordingly, the input voltage received by the voltage input circuit 120is not input to the amplifier 140, and the input current output from thecurrent input circuit 110 is input to the amplifier 140 to be amplified.

In the current measuring mode, when a level of the input current isgreater than a preset value, the current input circuit 110 may adjustthe level of the input current so that the level of the input current isless than the present value. The current input circuit 110 may generatea compensation current to adjust the level of the input current. Thecompensation current may compensate the input current so that the levelof the input current is adjusted to be within an operational range ofthe signal processing apparatus 100.

Hereinafter, the operation of the signal processing apparatus 100 willbe explained in detail.

FIGS. 2 and 3 are diagrams illustrating an example of a circuit forimplementing a signal processing apparatus 200.

Referring to FIGS. 2 and 3, the signal processing apparatus 200 measuresan input voltage and an input current using a single integral circuitconfiguration. The signal processing apparatuses 100 and 200 control aninput voltage and an input current input to a measuring circuit based ona control signal. FIG. 2 illustrates a switching connection performed bythe signal processing apparatus 200 in a voltage measuring mode. FIG. 3illustrates a switching connection performed by the signal processingapparatus 200 in a current measuring mode.

Hereinafter, the signal processing apparatus 200 operating in thevoltage measuring mode and the signal processing apparatus 200 operatingin the current measuring mode will be explained separately.

In the voltage measuring mode, the signal processing apparatus 200operates as described below.

Referring to FIG. 2, when the signal processing apparatus 200 operatesin the voltage measuring mode, the signal processing apparatus 200controls switches SW_I_(ip) 252, SW_I_(in) 254, SW_I_(op) 256, andSW_I_(on) 258 configured to control a flow of input currents I_(p) andI_(n) in the signal processing apparatus 200 to be opened. The inputcurrents I_(p) and I_(n) actually represent a single input current thatflows into the signal processing apparatus 200 as the input currentI_(p), and flows out of the signal processing apparatus 200 as the inputcurrent I_(n). Alternatively, the single input current may flow into thesignal processing apparatus 200 as the input current I_(n), and flow outof the signal processing apparatus 200 as the input current I_(p).

The signal processing apparatus 200 controls switches SW_V_(ip) 232 andSW_V_(in) 234 configured to control a flow of input voltages V_(ip) andV_(in) to be measured in the signal processing apparatus 200 to beclosed so that an output end of a second chopper 230 is connected to aninput end of an input element 240. The signal processing apparatus 200may control the second chopper 230 to output the input voltages V_(ip)and V_(in) directly, or to output the input voltages V_(ip) and V_(in)after converting a frequency component of the input voltages V_(ip) andV_(in). For example, the second chopper 230 may convert the frequencycomponent of the input voltages V_(ip) and V_(in) to have a frequencyhigher or lower than an original frequency of the frequency component ofthe input voltages V_(ip) and Vi_(n). In one example, the input element240 may be a voltage-current converter or a transistor. The inputelement 240 outputs a current based on a differential voltage betweenthe input voltages V_(ip) and V_(in).

The current output I_(v) from the input element 240 causes a currentI_(i) to flow through an input resistor 250, for example, R_(i),constituting a load element. A current mirror 260 mirrors the currentI_(i) flowing through the input resistor 250 to output a current I_(o)having a same level or an amplified level relative to the current I_(i).The current I_(o) output from the current mirror 260 generates voltagesat both ends of an output resistor 280, for example, R_(o). Based on thegenerated voltages, output voltages V_(op) and V_(on) are output fromoutput terminals of the signal processing apparatus 200.

In another example, the current I_(o) output from the current mirror 260is input to a third chopper 270, and the third chopper 270 converts afrequency component of the current I_(o). For example, the third chopper270 may perform a frequency demodulation on the current I_(o) having afrequency component that has been converted by the second chopper 230.

In one example, when a control signal (not shown) used to control afirst chopper 220, the second chopper 230, or the third chopper 270remains in a logic state High or a logic state Low, an input signal of achopper controlled by the control signal is directly output without thefrequency conversion being performed on the input signal. When thecontrol signal used to control the first chopper 220, the second chopper230, or the third chopper 270 is repetitively changed between the logicstate High and the logic state Low as time elapses, the input signal ofthe chopper is output after the frequency conversion is performed on theinput signal.

In another example, the signal processing apparatus 200 may also includean element to decrease an output impedance of the signal processingapparatus 200. For example, the signal processing apparatus 200 may alsoinclude a buffer (not shown) connected to the output terminals of thesignal processing apparatus 200 to decrease the output impedance.

In the current measuring mode, the signal processing apparatus 200operates as described below.

Referring to FIG. 3, when the signal processing apparatus 200 operatesin the current measuring mode, the signal processing apparatus 200controls an input voltage input to the signal processing apparatus 100to not be processed. The signal processing apparatus 200 controls theswitches SW_V_(ip) 232 and SW_V_(in) 234 that are used to connect inputsof the input element 240 to the input voltages V_(ip) and V_(in) in thevoltage measuring mode so that the inputs of the input element 240 areconnected to reference voltages V_(ip) _(_) _(b) and V_(in) _(_) _(b) inthe current measuring mode. The reference voltages V_(ip) _(_) _(b) andV_(in) _(_) _(b) may have the same voltage level as each other ordifferent voltage levels from each another. Also, the reference voltagesV_(ip) _(_) _(b) and V_(in) _(_) _(b) may have a fixed voltage level ora variable voltage level as time elapses.

When the input currents I_(ip) and I_(in) need to be amplified by arelatively high amplification level, the signal processing apparatus 200controls the switch SW_I_(ip) 252 controlling the flow of the inputcurrent I_(ip) and the switch SW_I_(in) 254 controlling the flow of theinput current I_(in) to be closed to allow the input currents I_(in) andI_(ip) to flow through the input resistor 250, for example, R_(i). Also,the signal processing apparatus 200 controls switches SW_I_(op) 256 andSW_I_(on) 258 to be opened to prevent the input currents I_(in) andI_(ip) from flowing through the output resistor 280, for example, R_(o).

When the input currents I_(ip) and I_(in) need to be amplified by arelatively low level, the signal processing apparatus 200 controls theswitches SW_I_(ip) 252 and SW_I_(in) 254 connected to opposite ends ofthe input resistor 250 to be opened to prevent the input currents I_(in)and I_(ip) from flowing through the input resistor 250, and controls theswitches SW_I_(op) 256 and SW_I_(on) 258 connected to opposite ends ofthe output resistor 280 to be closed to allow the input currents I_(in)and I_(ip) to flow through the output resistor 280.

In one example, when the input current to be measured exceeds anoperational range of the signal processing circuit 200, the signalprocessing apparatus 200 may control a level of the current flowing inthe signal processing apparatus 200 to be within the operational rangeusing an input current compensator 210. For example, when an inputcurrent to be measured includes a direct current (DC) current of 100microamperes (μA) and an alternating current (AC) current of 1 μA, and amaximum level of current allowed to flow through the input resistor 250is 10 μA, the input current compensator 210 outputs a compensationcurrent to flow in the circuit to offset the DC current of 100 μA. Dueto the compensation current output by the input current compensator 210,only the AC current of 1 μA flows through the input resistor 250.

To minimize noise flowing into the signal processing apparatus 200 in aprocess of amplifying the input current to be measured, the signalprocessing apparatus 200 may modulate the frequency component of theinput current using the first chopper 220, and demodulate the frequencycomponent using the third chopper 270. Alternatively, in response to amodulated frequency component of the input current to be measured, thesignal processing apparatus 200 may demodulate a modulated signal usingthe third chopper 270.

FIG. 4 is a diagram illustrating another example of a circuit forimplementing a signal processing apparatus 400.

Referring to FIG. 4, the signal processing apparatus 400 includes aninput voltage selector 410, an input current controller 420, an inputelement 430, and a load element 440. The signal processing apparatus 400is operable in a voltage measuring mode and a current measuring mode. Inone example, the signal processing apparatus 400 corresponds to atransconductance stage of an IA.

The input voltage selector 410 selects an input voltage from a pluralityof input voltages. In the example in FIG. 4, the plurality of inputvoltages include a target voltage to be measured and a preset referencevoltage. For example, a biosignal such as an ECG may be input as thetarget voltage to be measured. In FIG. 4, voltages V_TC_ip2 and V_TC_in2are the target voltage to be measured, and voltages Vref_TCp andVref_TCn are the preset reference voltage. The voltages Vref_TCp andVref_TCn may have the same voltage level as each other or differentvoltage levels from each another. Also, the voltages Vref_TCp andVref_TCn may have a fixed voltage level or a variable voltage level astime elapses.

The input voltage selector 410 is connected to the input element 430. Inthe example in FIG. 4, the input element 430 is a transistor having agate connected to the input voltage selector 410, but is not limitedthereto. The input voltage selector 410 selects an input voltage to beapplied to the input element 430 using a switch. The input element 430generates a current in response to the input voltage selected by theinput voltage selector 410 in the voltage measuring mode, and thus is atransconductance element. For example, the input element 430 may be atransistor and include a plurality of transconductance elements. Thus,the input element 430 converts the input voltage to be measured into acurrent. The input voltage to be applied to the input element 430 isdetermined by a control signal. In FIG. 4, REG_TC_SEL_ip andREG_TC_SEL_in are control signals that control the switching operationperformed by the input voltage selector 410. A source of the inputelement 430 is connected to a drain of a transistor PTOP, which forms acascode circuit with the input element 430. A drain of the input element430 is biased by a constant-current source providing a fixed currentib2. A source of the transistor PTOP is connected to a power supplyvoltage VDD. A gate of the transistor PTOP is biased by a voltageVoffset2.

The input current controller 420 controls an inflow of an input currentin conjunction with an operation of the input voltage selector 410. Forexample, the input current controller 420 blocks the inflow of the inputcurrent when an input voltage input to the signal processing apparatus400 is the target voltage to be measured by the input voltage selector410. The input current to be measured is input to the signal processingapparatus 400 by the input current controller 420. For example, abiosignal such as a PPG may be input to the signal processing apparatus400 as the input current. The input current controller 420 controls theinflow of the input current using a switch controlled by the controlsignal. The input current controller 420 allows the input current toflow into the signal processing apparatus 400 or block the inflow of theinput current based on a measurement mode. In FIG. 4, V_Current_ip andV_Current_in are the input current to be measured, and REG_TC_ch_disconis the control signal controlling the switching operation of the inputcurrent controller 420.

The load element 440 is functionally connected to the input currentcontroller 420 and the input element 430. For example, output terminalsof the input current controller 420 are connected to opposite ends ofthe load element 440, and one end of the input element 430 is connectedto the load element 440. In this example, “being functionally connected”includes “being directly connected to the input current controller 420and the input element 430” and “being affected by the input currentcontroller 420 and the input element 430”. For example, the load element440 may be a resistor having a resistance Ri2. A current flowing throughthe ends of the load element 440 may be changed due to the currentflowing through the input element 430 or the input current flowingthrough the input current controller 420.

In another example, the input current controller 420 may also include aninput current compensator 450 to adjust a level of the input current.The input current compensator 450 generates a compensation current toadjust the level of the input current. When a level of an input currentto be measured exceeds an operational range of the signal processingapparatus 400, the input current compensator 450 a compensation currentto offset the level of the input current to be within the operationalrange of the signal processing apparatus 400.

For example, the input current compensator 450 outputs the compensationcurrent to decrease a DC level of the input current to be within apreset range. To decrease the DC level of the input current, the inputcurrent compensator 450 outputs a compensation current having a negativeDC level, for example, −3 milliamperes (mA). The level of the inputcurrent is adjusted by adding the input current flowing into the signalprocessing apparatus 400 and the compensation current output by theinput current compensator 450.

The input current compensator 450 may operate in a manual adjustmentmode and an automatic adjustment mode. For example, in the manualadjustment mode, the input current compensator 450 manually adjusts thelevel of the input current under a control of a user. In the automaticadjustment mode, the input current compensator 450 adaptively adjuststhe level of the input current based on an output signal of the signalprocessing apparatus 400. For example, in the automatic adjustment mode,the input current compensator 450 may extract a signal of alow-frequency band from the output signal of the signal processingapparatus 400, and determine whether the level of the input current isto be adjusted based on a level of the extracted signal of thelow-frequency band. Based on a result of the determining, the inputcurrent compensator 450 determines a level of the compensation currentto be used to adjust the level of the input current, and adjusts thelevel of the input current flowing in the signal processing apparatus400 by outputting the compensation current having the determined level.

In the automatic adjustment mode, the signal processing apparatus 400may also include an input current compensation controller (not shown) togenerate a control signal used to control the input current compensator450. The input current compensation controller controls the level of thecompensation current output by the input current compensator 450 basedon the output signal of the signal processing apparatus 400. In oneexample, the signal processing apparatus 400 includes a low-pass filter(not shown) to output the signal of the low-frequency band from theoutput signal of the signal processing apparatus 400, and a comparator(not shown) to compare a level of an output signal of the low-passfilter to a level of a preset reference signal and output a result ofthe comparing to the input current compensation controller. The inputcurrent compensation controller generates the control signal to controlthe input current compensator 450 based on the result of the comparing.A detailed explanation of the input current compensation controller willbe provided with reference to FIG. 12.

In another example, the input current controller 420 also includes achopper 460 to modulate a frequency component of the input current basedon a control signal. The chopper 460 changes connections between inputends and output ends of the input current controller 420 based on thecontrol signal. Low-frequency noise, 1/f noise, or flicker noise may bereduced when the chopper 460 performs the modulation on the frequencycomponent of the input current. For example, the low-frequency noiseoccurring in the signal of the low-frequency band may be reduced whenthe input current is modulated into a signal of a high-frequency band bythe chopper 460. When the chopper 460 does not perform the abovemodulation, the chopper 460 operates as a switch to allow and block theinflow of the input current.

Hereinafter, the signal processing apparatus 400 operating in thevoltage measuring mode and the signal processing apparatus 400 operatingin the current measuring mode will be described.

In the voltage measuring mode, the signal processing apparatus 400operates as described below.

In the voltage measuring mode, the signal apparatus 400 blocks theinflow of the input current and selects a voltage to be measured as theinput voltage.

The input voltage selector 410 applies an input voltage to be measuredto the input element 430. For example, the input current selector 410applies an input voltage V_TC_ip2 to be measured to a gate node V_Gp ofone input element 430, and applies an input voltage V_TC_in2 to bemeasured to a gate node V_Gn of the other input element 430. The inputvoltage V_TC_ip2 and the input voltage V_TC_in2 have a differentialinput relationship. When control signals REG_TC_SEL_ip and REG_TC_SEL_inhave a logically high value, for example, H, the input voltage V_TC_ip2is applied to the gate node V_Gp and the input voltage V_TC_in2 isapplied to the gate node V_Gn so that the input voltage to be measuredis input to the signal processing apparatus 400.

Due to the input voltages V_TC_ip2 and V_TC_in2 having the differentialinput relationship, the current flowing through the ends of the loadelement 440 may be changed.

In response to the applied input voltage, one input element 430generates a current flowing from a source node V_Sp to a drain nodeV_Dp, and another input element 430 generates a current flowing from asource node V_Sn to a drain node V_Dn. The drain node V_Dp is connectedto an output node V_TC_op2 of the signal processing apparatus 400, andthe drain node V_Dn is connected to an output node V_TC_on2 of thesignal processing apparatus 400.

The input current controller 420 blocks the inflow of the input currentinto the signal processing apparatus 400 in the voltage measuring mode.For example, when a control signal REG_TC_ch_discon has a logically highvalue, switches (not shown) included in the chopper 460 of the inputcurrent controller 420 are opened so that the input current does notflow into the ends of the load element 440.

In the current measuring mode, the signal processing apparatus 400operates as described below.

In the current measuring mode, the signal processing apparatus 400allows the inflow of the input current to be measured into the signalprocessing apparatus 400, and selects the preset reference voltage asthe input voltage in lieu of the voltage to be measured.

The input voltage selector 410 applies a reference voltage having afixed voltage level to the input element 430. For example, when thecontrol signal REG_TC_SEL_in has a logically low value, for example, L,the input voltage selector 410 applies a reference voltage Vref_TCphaving the fixed voltage level to the gate node V_Gp of one inputelement 430, and applies a reference voltage Vref_TCn having the fixedvoltage level to the gate node V_Gn of the other input element 430.

Since a fixed current ib2 flows through each of the input elements 430,a constant voltage level may be maintained at each of the source nodesV_Sp and V_Sn of the input elements 430. By adjusting a level of thereference voltage Vref_TCp, a voltage having a desired level may beprovided to the source node V_Sp, and by adjusting a level of thereference voltage Vref_TCn, a voltage having a desired level may beprovided to the source node V_Sn.

The input current controller 420 allows the inflow of the input currentto be measured into the signal processing apparatus 400. For example,the input current controller 420 allows an inflow of input currentsV_Current_ip and V_Current_in to be measured. The input currentV_Current_ip and the input current V_Current_in may have a differentialinput relationship. When the control signal REG_TC_ch_discon has alogically low value, the switches included in the chopper 460 areconnected so that the input end and the output end are connected in thechopper 460.

Due to the input currents V_TC_ip2 and V_TC_in2 having the differentialinput relationship, the current flowing through the ends of the loadelement 440 may be changed.

Based on the control signal REG_TC_ch_discon, the chopper 460 mayoperate as a switch connecting the input end of the chopper 460 with theoutput end of the chopper 460 and modulate the frequency component ofthe input current through a periodic switching operation.

In another example, the input current controller 420 may also includethe input current compensator 450 to adjust a level of the inputcurrent. When the level of the input current to be measured is beyond anoperational range of the signal processing apparatus 400, the inputcurrent compensator 450 outputs a compensation current to offset thelevel of the input current to be within the operational range of thesignal processing apparatus 400. Based on the compensation current, theinput current is changed into a signal having a current level that canbe handled by elements of the signal processing apparatus 400.

FIG. 5 is a diagram illustrating an example of a signal processingapparatus 500 operating in a voltage measuring mode.

Referring to FIG. 5, the signal processing apparatus 500 includes atransconductance stage 510 and a transimpedance stage 520. Thetransconductance stage 510 corresponds to the signal processingapparatus 400 of FIG. 4. The transconductance stage 510 may operate ineither the voltage measuring mode or a current measuring mode. Thetransconductance stage 510 controls an inflow of an input current andselects a type of an input voltage to be applied based on a measuringmode.

In FIG. 5, the signal processing apparatus 500 measures an ECG in thevoltage measuring mode. ECG_ip and ECG_in are ECG signals measured by asensor 550 such as a bioelectrode. In the voltage measuring mode, thetransconductance stage 510 selects a voltage to be measured as an inputvoltage and blocks the inflow of the input current. For example, in thevoltage measuring mode, the transconductance stage 510 selects inputvoltages V_TC_ip2 and V_TC_in2 to be measured to be applied to aninternal input element, and block inflows of input currents V_Current_ipand V_Current_in. The transconductance stage 510 selects the type of theinput voltage based on a control signal REG_TC_SEL_in. Thetransconductance stage 510 controls a switch used to determine whetherthe input current is allowed to flow based on a control signalREG_TC_ch_discon.

The transimpedance stage 520 generates output voltages V_TI_op2 andV_TI_on2 based on a current output from the transconductance stage 510.The transimpedance stage 520 may include a current mirror circuit.

The signal processing apparatus 500 may also include an input chopper530 to modulate a frequency component of the input voltage of thetransconductance stage 510 in the voltage measuring mode. The inputchopper 530 modulates the input voltage into a signal of ahigh-frequency band, thereby reducing low-frequency noise. A controlsignal REG_input_ch_discon determines whether the input chopper 530operates. A control signal f_ch_i controls a connection of each switchincluded in the input chopper 530.

The transimpedance stage 520 includes an output chopper 540 todemodulate into a signal of a low-frequency band the input signal thathas been modulated into the signal of the high-frequency band by theinput chopper 530. A control signal f_ch_o controls a connection of eachswitch included in the output chopper 540. In one example, the controlsignal f_ch_o applied to the output chopper 540 has the same signalwaveform as the control signal f_ch_i applied to the input chopper 530.

FIGS. 6A and 6B are diagrams illustrating examples of operating an inputchopper based on a control signal.

The control signal REG_input_ch_discon determines whether the inputchopper operates. For example, when the control signalREG_input_ch_discon is in a logically high state H as shown in FIG. 6A,all switches included in the input chopper are turned off so that aconnection between an input end and an output end of the input chopperis blocked. Conversely, the input chopper operates when the controlsignal REG_input_ch_discon is in a logically low state L as shown inFIG. 6B. When the input chopper operates, operations of the switchesincluded in the input chopper are controlled based on a control signalf_input_ch. A control signal f_input_ch_bar (not shown) that is aninverse waveform of the control signal f_input_ch may be generated basedon the control signal f_input_ch. Connections among the switchesincluded in the input chopper may be changed based on the control signalf_input_ch and the control signal f_input_ch_bar.

FIGS. 7A through 7C are diagrams illustrating examples of a controlsignal input for each chopper in a voltage measuring mode.

An example of a control signal f_ch_i applied to an input chopper isillustrated in FIG. 7A. An example of a control signal f_ch_o applied toan output chopper is illustrated in FIG. 7B. An example of a controlsignal f_TC_ch applied to a chopper included in an input currentcontroller is illustrated in FIG. 7C. In the voltage measuring mode, aninput voltage is modulated into a signal of a high-frequency band by theinput chopper, and the modulated input voltage is demodulated into asignal of a low-frequency band by the output chopper. In the voltagemeasuring mode, connections of switches included in the chopper of theinput current controller are blocked, so the control signal f_TC_ch isin a logically low state.

FIG. 8 is a diagram illustrating an example of a signal processingapparatus 800 operating in a current measuring mode. FIG. 9 is a diagramillustrating an example of a signal processing apparatus 900 operatingin a current measuring mode.

In FIG. 8, the signal processing apparatus 800 measures a photovoltaicmode PPG in the current measuring mode. Currents V_Current_ip andV_Current_in output from a light detector 810 of FIG. 8 are input to thetransconductance stage 510.

In FIG. 9, the signal processing apparatus 900 measures aphotoconductive mode PPG in the current measuring mode. A currentV_Current_ip output from a light detector 910 of FIG. 9 is input to thetransconductance stage 510.

Referring to FIGS. 8 and 9, in the current measuring mode, thetransconductance stage 510 applies reference voltages Vref_TCp andVref_TCn, each preset as an input voltage, to internal input elements ofthe transconductance stage 510. Based on a control signal REG_TC_SEL_in,the input voltage applied to an input element is determined and inputvoltages V_TC_in2 and V_TC_ip2 input to the transconductance stage 510may be blocked. A control signal REG_TC_ch_discon is used to determinewhether an input current is allowed to flow into the transconductancestage 510. A control signal f_TC_ch is used to control a chopperincluded in the transconductance stage 510. Through switching operationsof switches included in the chopper, the input current may be modulatedinto a signal of a high-frequency band.

The transimpedance stage 520 includes the output chopper 540 todemodulate into a low-frequency band an input signal that has beenmodulated into the signal of the high-frequency band by the chopperincluded in the transconductance stage 510. A control signal f_ch_o isused to control a connection of each switch included in the outputchopper 540. In one example, the control signal f_ch_o applied to theoutput chopper 540 has the same waveform as a control signal f_TC_chapplied to the chopper of the transconductance stage 510.

FIGS. 10A through 11C are diagrams illustrating examples of a controlsignal input for each chopper in a current measuring mode.

Examples of a control signal applied to each chopper when the chopper isoperated in the current measuring mode are illustrated in FIGS. 10Athrough 10C.

An example of control signal f_ch_i applied to an input chopper is shownin FIG. 10A. An example of control signal f_ch_o applied to an outputchopper is shown in FIG. 10B. An example of a control signal f_TC_chapplied to a chopper included in a transconductance stage is shown inFIG. 10C. In the current measuring mode, an input current is modulatedinto a signal of a high-frequency band by the chopper of thetransconductance stage, and the modulated input current is demodulatedinto a signal of a low-frequency band by the output chopper. In acurrent measuring mode, the input chopper is not used, so the controlsignal f_ch_i is in a logically low state.

In one example, when the control signal f_TC_ch is in a logically highstate, a first input end is connected to a first output end and a secondinput end is connected to a second output end in the chopper included inthe transconductance stage, and when the control signal f_TC_ch is inthe logically low state, the first input end is connected to the secondoutput end and the second input end is connected to the first output endin the chopper included in the transconductance stage.

Examples of a control signal applied to each chopper when the chopper isnot operated in the current measuring mode are illustrated in FIGS. 11Athrough 11C.

An example of a control signal f_ch_i applied to an input chopper isshown in FIG. 11A. An example of a control signal f_ch_o applied to anoutput chopper is shown in FIG. 11B. An example of a control signalf_TC_ch applied to a chopper included in a transconductance stage isshown in FIG. 11C. In one example, when the chopper is not operated,each of the control signal f_ch_i, the control signal f_ch_o, and thecontrol signal f_TC_ch are in a logically low state.

FIG. 12 is a diagram illustrating an example of an operation performedby a signal processing apparatus 1200 in an automatic adjustment modefor adjusting an input current level.

Referring to FIG. 12, the signal processing apparatus 1200 includes theinput current compensator 210 to adjust the input current level in acurrent measuring mode. In one example, the signal processing apparatus1200 also includes a control circuit 1210 to control the input currentcompensator 210 based on an output signal of the signal processingapparatus 1200. The control circuit 1210 includes an input currentcompensation controller 1250, a low-pass filter 1220, a first comparator1230, and a second comparator 1240.

In one example, an output end of the signal processing apparatus 1200 isconnected to an input end of the low-pass filter 1220, and an output endof the low-pass filter 1220 is connected to an input end of each of thefirst comparator 1230 and the second comparator 1240. An output end ofeach of the first comparator 1230 and the second comparator 1240 isconnected to an input end of the input current compensation controller1250, and an output end of the input current compensation controller1250 is connected to the input current compensator 210.

The low-pass filter 1220 extracts a signal of a low-frequency band fromoutput signals V_(op) and V_(on) of the signal processing apparatus1200. For example, the signal processing apparatus 1200 may extract asignal of a frequency band less than or equal to 0.1 hertz (Hz) from theoutput signal of the signal processing apparatus 1200 using the low-passfilter 1220. A signal V_LPF of the low-frequency band output from thelow-pass filter 1220 is input to the first comparator 1230 and thesecond comparator 1240.

The first comparator 1230 compares the signal V_LPF of the low-frequencyband to a control signal Vlimit_H, and outputs a signal V_(comp) _(_)_(H) indicating a result of the comparing. The second comparator 1240compares the signal V_LPF of the low-frequency band to a control signalVlimit_L, and outputs a signal V_(comp) _(_) _(L) indicating a result ofthe comparing. An upper limit of a voltage range of the extracted signalof the low-frequency band is set by the control signal Vlimit_H, and alower limit of the voltage range of the extracted signal of thelow-frequency band is set by the control signal Vlimit_L.

In one example, when the signal V_LPF output from the low-pass filter1220 is in a range between the control signal Vlimit_L and the controlsignal Vlimit_H, for example, Vlimit_L<V_LPF<Vlimit_H, the signalV_(comp) _(_) _(H) output from the first comparator 1230 and the signalV_(comp) _(_) _(L) output from the second comparator 1240 have alogically low value. In this example, the control signal output from theinput current compensation controller 1250 to the input currentcompensator 210 remains the same as a previous control signal outputfrom the input current compensation controller 1250.

In another example, when a level of the signal V_LPF output from thelow-pass filter 1220 is greater than a level of the control signalVlimit_H, the first comparator 1230 outputs a logically high value, andthe second comparator 1240 outputs a logically low value. In thisexample, the input current compensation controller 1250 outputs, to theinput current compensator 210, a control signal to decrease the level ofthe signal V_LPF.

In another example, when the level of the signal V_LPF output from thelow-pass filter 1220 is less than the level of the control signalVlimit_L, the first comparator 1230 outputs a logically low value andthe second comparator 1240 outputs a logically high value. In thisexample, the input current compensation controller 1250 outputs, to theinput current compensator 210, a control signal to increase the level ofthe signal V_LPF.

As described above, the input current compensation controller 1250automatically controls a level of a compensation current output by theinput current compensator 210 based on an output signal of the signalprocessing apparatus 1200. Other operations of the signal processingapparatus 1200 of FIG. 12 were previously explained with reference toFIGS. 2 and 3.

FIG. 13 is a diagram illustrating an example of a configuration of atransimpedance stage 1300.

The transimpedance stage 1300 generates output voltages V_TI_op2 andV_TI_on2 based on a current output from a transconductance stage. Thetransimpedance stage 1300 includes a current mirror circuit constitutedby all of the elements in FIG. 13 except for the two transistors at thetop that receive V_TC_op2 and V_TC_on2 and the output choppers 1310. Thetransimpedance stage 1300 includes the output choppers 1310 todemodulate into a signal of a low-frequency band an input signal thathas been modulated into a signal of a high-frequency band by an inputchopper or a chopper included in the transconductance stage. The twooutput choppers 1310 enable the input signal to be demodulated moreaccurately through two frequency demodulation processes. In FIG. 14, VDDdenotes a power supply voltage, CASP denotes PMOS cascode transistors,Ro denotes an output resistance, and CASN denotes NMOS cascodetransistors.

FIG. 14 is a flowchart illustrating an example of a signal processingmethod.

In operation 1410, a signal processing apparatus selects a voltagemeasuring mode and a current measuring mode. The signal processingapparatus controls an inflow of an input current or selects a type of aninput voltage to be applied to an input element based on the selectedmeasuring mode.

In operation 1420, the signal processing apparatus determines whetherthe voltage measuring mode or the current measuring mode has beenselected.

When it is determined in operation 1420 that the voltage measuring modehas been selected, the signal processing apparatus blocks the inflow ofthe input current and selects an input voltage to be measured inoperation 1430. The signal processing apparatus applies the inputvoltage to be measured to an input element, and blocks the inflow of theinput current by turning off a switch used to control the inflow of theinput current.

When it is determined in operation 1420 that the current measuring modehas been selected, the signal processing apparatus selects a presetreference voltage and allows the inflow of the input current inoperation 1440. The signal processing apparatus applies the presetreference voltage, which may have a fixed voltage level, to the inputelement, and allows the inflow of the input current by turning on theswitch used control the inflow of the input current. Also, the signalprocessing apparatus may modulate the input current into a signal of ahigh-frequency band using a chopper. The input current modulated intothe signal of the high-frequency band may be demodulated into a signalof a low-frequency band by an output chopper.

In one example, the signal processing method may also include operation1450 of adjusting a level of the input current to be within a presetrange. When the level of the input current is outside an operationalrange of the signal processing apparatus, the signal processingapparatus may generate a compensation current and adjust the inputcurrent to a signal having an appropriate level using the compensationcurrent. The signal processing apparatus may adjust the level of theinput current in a manual adjustment mode or in an automatic adjustmentmode. In the manual adjustment mode, the signal processing apparatusmanually adjusts the level of the input current under the control of auser. In the automatic adjustment mode, the signal processing apparatusdetermines a level of the compensation current based on the outputsignal of the signal processing apparatus. For example, the signalprocessing apparatus may extract a signal of a low-frequency band fromthe output signal of the signal processing apparatus, and determine asign and a level of the compensation current based on whether a level ofthe extracted signal is within a preset voltage range.

FIGS. 15 through 16B are diagrams illustrating examples of a wearabledevice including a signal processing apparatus.

Each signal processing apparatus described with reference to FIGS. 1through 14 may be embedded in a wearable device 1510. In one example,the wearable device 1510 is a device to be worn on a wrist of a userprovided in the form of a watch of a bracelet. The wearable device 1510measures various biosignals from a body of a user 1520, and the measuredbiosignals are processed by a signal processing apparatus.

The wearable device 1510 includes various sensors for measuring abiosignal of the user 1520. For example, the wearable device 1510includes a bioelectrode for measuring an ECG, a sensor for measuring aPPG, a sensor for measuring a heart rate of the user 1520, a sensor formeasuring a body temperature, and a sensor for measuring a skinhumidity.

Based on a measurement method, the biosignal may be detected as avoltage signal or a current signal, and an attribute such as a frequencybandwidth may vary in the biosignal. The signal processing apparatusprocesses a biosignal having a diversified attribute and converts thebiosignal into a state in which the wearable device 1510 can easilyanalyze the biosignal. The signal processing apparatus may operate in avoltage measuring mode or in a current measuring mode. Based on ameasurement mode, the signal processing apparatus controls connectionsbetween internal elements of the signal processing apparatus to analyzebiosignals each having a different attribute.

The signal processing apparatus measures a current signal and a voltagesignal by controlling the connection between the internal elements whilesharing the internal elements. For example, in a process of measuring avoltage signal such as an ECG, the signal processing apparatus controlsthe connections between the internal elements to amplify the voltagesignal in the voltage measuring mode. In contrast, in a process ofmeasuring a current signal such as a PPG, the signal processingapparatus controls the connections between the internal elements toamplify the current signal in the current measuring mode.

FIG. 15 illustrates an example of the wearable device 1510 measuring theECG from the body of the user 1520. For example, when the user 1520 iswearing the wearable device 1510 on a left wrist, and touches a sensor1530 of the wearable device 1510 with a forefinger of a right hand, theECG is measured from the user 1520. The sensor 1530 may be, for example,a bioelectrode for measuring the ECG. The wearable device 1510 maydetermine a heart rate of the user 1520, and display heart rateinformation and the ECG on a display.

FIGS. 16A and 16B illustrate examples of a front side and a rear side ofthe wearable device 1510 of FIG. 15.

Referring to FIG. 16A, the wearable device 1510 includes fasteners 1660and 1670 to fasten the wearable device 1510 on a wrist of a user. Thewearable device 1510 includes a first electrode 1620 to measure an ECG.The first electrode 1620 corresponds to the sensor 1530 of FIG. 15.Also, the wearable device 1510 includes a body 1610 including a signalprocessing apparatus and additional elements. The wearable device 1510includes a display 1615 to display a measured biosignal and an analysisresult of the biosignal. The display 1615 is disposed on an upperportion of the body 1610.

Referring to FIG. 16B, the wearable device 1510 includes a secondelectrode 1630 to measure the ECG. The second electrode 1630 iselectrically isolated from the first electrode 1620, and the ECG ismeasured from an electrical path through the user's body between thefirst electrode 1620 and the second electrode 1630. The wearable device1510 includes a reference electrode 1650 to measure a reference voltagefor measuring the ECG.

Also, the wearable device 1510 includes an optical sensor 1640 tomeasure a current measurement-based biosignal such as a PPG and a bloodoxygen saturation. The optical sensor 1640 includes a light source unitto radiate a light signal of a predetermined wavelength onto the body ofthe user, and a light detector to detect a biosignal based on the lightsignal. Hereinafter, the optical sensor 1640 will be explained in detailwith reference to FIG. 17.

FIG. 17 is a diagram illustrating an example of a structure of anoptical sensor 1710.

The optical sensor 1710 senses a current measurement-based biosignalsuch as a PPG and a blood oxygen saturation. The optical sensor 1710corresponds to the optical sensor 1640 of FIG. 16B. The optical sensor1710 includes a light source unit to radiate a light signal onto a bodyof a user, and a light detector 1740 to detect a biosignal based on thelight signal. The light source unit may include a plurality of lightsources, and may have an array structure in which the light sources arearranged in a predetermined direction. In FIG. 17, as one example, thelight source unit includes a first light source array 1720 and a secondlight source array 1730. The first light source array 1720 includeslight sources LS11, LS21, LS31, and LS41. The second light source array1730 includes light sources LS12, LS22, LS32, and LS42.

In the example in FIG. 17, the light detector 1740 is disposed betweenthe first light source array 1720 and the second light source array1730. The light detector 1740 includes a plurality of photo detectors,and has a structure in which the photo detectors are arranged in apredetermined direction. In FIG. 17, as one example, the light detector1740 includes photo detectors PD1, PD2, PD3, and PD4.

Based on a physical characteristic of a user, a position of a radialartery 1750 in a wrist may vary. An optimal biosignal may be acquiredusing the array structure of the light source unit and the arraystructure of the light detector 1740. For example, when the user wearsthe wearable device 1510, the radial artery 1750 may be located close tothe photo detector PD2. In this example, a biosignal measured by thephoto detector PD2 will have a higher amplitude or fluctuation whencompared to a biosignal measured by the photo detectors PD1, PD3, andPD4.

The light sources included in the first light source array 1720 and thelight sources included in the second light source array 1730 may radiatelight having the same wavelength or light having different wavelengths.For example, when measuring a blood oxygen saturation of the user, thelight sources included in the first light source array 1720 radiate redlight, and the light sources included in the second light source array1730 radiate infrared light.

FIG. 18 is a diagram illustrating an example of a configuration of asignal processing apparatus 1810.

The signal processing apparatus 1810 measures various types ofbiosignals from a body of a user and processes the measured biosignals.The signal processing apparatus 1810 includes various sensors formeasuring a biosignal. For example, the signal processing apparatus 1810includes electrodes for measuring a voltage measurement-based biosignal,and an optical sensor for measuring a current measurement-basedbiosignal. The signal processing apparatus 1810 may operate in a voltagemeasuring mode or in a current measuring mode. Based on a measurementmode, the signal processing apparatus 1810 controls connections betweeninternal elements of the signal processing apparatus 1810 to amplifybiosignals having different attributes.

Referring to FIG. 18, the signal processing apparatus 1810 includes alight source unit 1840, a light detector 1850, a bioelectrode 1880, asignal processor 1870, and a controller 1820.

The light source unit 1840 radiates light onto the body of the user. Thelight source unit 1840 includes a plurality of light sources, and has astructure in which the light sources are arranged in a predetermineddirection. The light sources form a plurality of light source arraystructures. Light sources included in each of the light source arraystructures may radiate light having the same wavelength, or light havingdifferent wavelengths. In the example in FIG. 18, a first light sourcearray includes light sources LS11, LS21, LS31, and LS41, and a secondlight source array includes light sources LS12, LS22, LS32, and LS42.For example, the light sources LS11 and LS12 may radiate light havingthe same wavelength, or light having different wavelengths.

In one example, the light detector 1850 detects a first biosignalmeasured based on a light signal output from the light source unit 1840.For example, the first biosignal may be a PPG signal or a signalincluding SpO₂ information. The light detector 1850 includes a pluralityof photo detectors, and has an array structure in which the photodetectors are arranged in a predetermined direction. In the example inFIG. 18, the light detector 1850 includes photo detectors PD1, PD2, PD3,and PD4.

The controller 1820 controls a light source driver 1830 to drive thelight source unit 1840, a multiplexer 1860, and the signal processor1870. The controller 1820 uses the multiplexer 1860 to controlconnections between the signal processor 1870 and the photo detectorsPD1, PD2, PD3, and PD4. The photo detectors PD1, PD2, PD3, and PD4 areconnected to the multiplexer 1860. The multiplexer 1860 may apply, tothe signal processor 1870, predetermined biosignals, for example, firstbiosignals I_(in) and I_(ip) among a plurality of first biosignalsoutput from the photo detectors PD1, PD2, PD3, and PD4 under a controlof the controller 1820.

The bioelectrode 1880 detects a second biosignal measured based on avoltage signal. For example, the second biosignal may be an ECG signal.In the example in FIG. 18, the bioelectrode 1880 includes a firstelectrode and a second electrode, and detects the second biosignalmeasured from an electrical path through the user's body between thefirst electrode and the second electrode. The first electrode and thesecond electrode are connected to an input end of the signal processor1870, and respectively apply signals V_(ip) and V_(in) to the signalprocessor 1870.

The signal processor 1870 amplifies the first biosignal or the secondbiosignal depending on a measurement mode. Signals V_(op) and V_(on) areoutput signals of the signal processor 1870. Detailed descriptions ofthe operations performed by the signal processor 1870 have beendescribed with reference to FIGS. 1 through 14. The controller 1820controls the measurement mode of the signal processor 1870, which may bea current measuring mode or a voltage measuring mode.

In the current measuring mode, the controller 1820 controls the signalprocessor 1870 to amplify the first biosignal. The controller 1820controls a connection between the signal processor 1870 and thebioelectrode 1880 to prevent the signal processor 1870 from amplifyingthe second biosignal output from the bioelectrode 1880, and to input thefirst biosignal output from the light detector 1850 to the signalprocessor 1870 through the multiplexer 1860.

In the voltage measuring mode, the controller 1820 controls the signalprocessor 1870 to amplify the second biosignal. The controller 1820 usesthe multiplexer 1860 to block the first biosignal output from the lightdetector 1850 from being input to the signal processor 1870. Also, thecontroller 1820 controls the signal processor to amplify the secondbiosignal output from the bioelectrode 1880.

Additionally, the controller 1820 may select at least one light sourcefor measuring the biosignal from the light sources LS11 to LS42 includedin the light source unit 1840. The controller 1820 may sequentiallyactivate at least one light source among the light sources during eachof a plurality of time intervals, and select a light source formeasuring the first biosignal from the light sources LS11 to LS42 basedon a level of a signal output from the light detector 1850 during eachtime interval.

In one example, the controller 1820 controls the light source driver1830 to activate only the light sources LS11 and LS12 during a firsttime interval, and controls the multiplexer 1860 to apply an outputsignal of the photo detector PD1 to an input terminal of the signalprocessor 1870. During a second time interval following the first timeinterval, the controller 1820 activates only the light sources LS21 andLS22, and controls the multiplexer 1860 to apply an output signal of thephoto detector PD2 to the input terminal of the signal processor 1870.During a third time interval following the second time interval, thecontroller 1820 activates only the light sources LS31 and LS32, andcontrols the multiplexer 1860 to apply an output signal of the photodetector PD3 to the input terminal of the signal processor 1870. Duringa fourth time interval provided following the third time interval, thecontroller 1820 activates only the light sources LS41 and LS42, andcontrols the multiplexer 1860 to apply an output signal of the photodetector PD4 to the input terminal of the signal processor 1870.

The controller 1820 may repetitively perform the aforementionedprocedure and analyze the level of the signal output by the lightdetector during each time interval, thereby determining a pair of alight source and a photo detector to be used for measuring the firstbiosignal. The controller 1820 may operate only the determined lightsource and the determined photo detector, and control the multiplexer1860 so that an output signal of the determined photo detector isapplied to the input terminal of the signal processor 1870. For example,when the level of the signal output by the photo detector PD2 during thesecond time interval is higher than levels of the signals output by thephoto detectors PD1, PD3, and PD4 during the first, third, and fourthtime intervals, the controller 1820 may determine the light sources LS21and LS22 as light sources for measuring the second biosignal, andcontrol the multiplexer 1860 to apply an output signal of the photodetector PD2 to the signal processor 1870.

In another example, the controller 1820 may periodically perform theaforementioned procedure of determining the pair of light source andphoto detector, thereby determining an optimal sensing position formeasuring the first biosignal. Based on light emitting timinginformation of the light sources LS11 to LS42 received from thecontroller 1820, the signal processor 1870 may determine a time intervalduring which the determined light source emits light, and amplify thesignal of the photo detector input to the signal processor 1870 onlyduring the determined time interval, thereby amplifying only the signalof the determined photo detector.

The controllers 130 and 1820 in FIGS. 1 and 18, the input currentcompensators 210 and 450 in FIGS. 2-4 and 12, the input currentcompensation controller 1250 in FIG. 12, and the light source driver1830 and the multiplexer 1860 in FIG. 18 that perform the operationsdescribed herein with respect to FIGS. 1-18 are implemented by hardwarecomponents. Examples of hardware components include controllers,generators, drivers, and any other electronic components known to one ofordinary skill in the art. In one example, the hardware components areimplemented by one or more processors or computers. A processor orcomputer is implemented by one or more processing elements, such as anarray of logic gates, a controller and an arithmetic logic unit, adigital signal processor, a microcomputer, a programmable logiccontroller, a field-programmable gate array, a programmable logic array,a microprocessor, or any other device or combination of devices known toone of ordinary skill in the art that is capable of responding to andexecuting instructions in a defined manner to achieve a desired result.In one example, a processor or computer includes, or is connected to,one or more memories storing instructions or software that are executedby the processor or computer. Hardware components implemented by aprocessor or computer execute instructions or software, such as anoperating system (OS) and one or more software applications that run onthe OS, to perform the operations described herein with respect to FIGS.1-18. The hardware components also access, manipulate, process, create,and store data in response to execution of the instructions or software.For simplicity, the singular term “processor” or “computer” may be usedin the description of the examples described herein, but in otherexamples multiple processors or computers are used, or a processor orcomputer includes multiple processing elements, or multiple types ofprocessing elements, or both. In one example, a hardware componentincludes multiple processors, and in another example, a hardwarecomponent includes a processor and a controller. A hardware componenthas any one or more of different processing configurations, examples ofwhich include a single processor, independent processors, parallelprocessors, single-instruction single-data (SISD) multiprocessing,single-instruction multiple-data (SIMD) multiprocessing,multiple-instruction single-data (MISD) multiprocessing, andmultiple-instruction multiple-data (MIMD) multiprocessing.

The method illustrated in FIG. 14 that performs the operations describedherein with respect to FIGS. 1-18 is performed by a processor or acomputer as described above executing instructions or software toperform the operations described herein.

Instructions or software to control a processor or computer to implementthe hardware components and perform the methods as described above arewritten as computer programs, code segments, instructions or anycombination thereof, for individually or collectively instructing orconfiguring the processor or computer to operate as a machine orspecial-purpose computer to perform the operations performed by thehardware components and the methods as described above. In one example,the instructions or software include machine code that is directlyexecuted by the processor or computer, such as machine code produced bya compiler. In another example, the instructions or software includehigher-level code that is executed by the processor or computer using aninterpreter. Programmers of ordinary skill in the art can readily writethe instructions or software based on the block diagrams and the flowcharts illustrated in the drawings and the corresponding descriptions inthe specification, which disclose algorithms for performing theoperations performed by the hardware components and the methods asdescribed above.

The instructions or software to control a processor or computer toimplement the hardware components and perform the methods as describedabove, and any associated data, data files, and data structures, arerecorded, stored, or fixed in or on one or more non-transitorycomputer-readable storage media. Examples of a non-transitorycomputer-readable storage medium include read-only memory (ROM),random-access memory (RAM), flash memory, CD-ROMs, CD-Rs, CD+Rs, CD-RWs,CD+RWs, DVD-ROMs, DVD-Rs, DVD+Rs, DVD-RWs, DVD+RWs, DVD-RAMs, BD-ROMs,BD-Rs, BD-R LTHs, BD-REs, magnetic tapes, floppy disks, magneto-opticaldata storage devices, optical data storage devices, hard disks,solid-state disks, and any device known to one of ordinary skill in theart that is capable of storing the instructions or software and anyassociated data, data files, and data structures in a non-transitorymanner and providing the instructions or software and any associateddata, data files, and data structures to a processor or computer so thatthe processor or computer can execute the instructions. In one example,the instructions or software and any associated data, data files, anddata structures are distributed over network-coupled computer systems sothat the instructions and software and any associated data, data files,and data structures are stored, accessed, and executed in a distributedfashion by the processor or computer.

While this disclosure includes specific examples, it will be apparent toone of ordinary skill in the art that various changes in form anddetails may be made in these examples without departing from the spiritand scope of the claims and their equivalents. The examples describedherein are to be considered in a descriptive sense only, and not forpurposes of limitation. Descriptions of features or aspects in eachexample are to be considered as being applicable to similar features oraspects in other examples. Suitable results may be achieved if thedescribed techniques are performed in a different order, and/or ifcomponents in a described system, architecture, device, or circuit arecombined in a different manner, and/or replaced or supplemented by othercomponents or their equivalents. Therefore, the scope of the disclosureis defined not by the detailed description, but by the claims and theirequivalents, and all variations within the scope of the claims and theirequivalents are to be construed as being included in the disclosure.

What is claimed is:
 1. A signal processing apparatus comprising: aninput voltage selector, including first plural switches, configured to:select, using the first plural switches and dependent on an operationmode of the input voltage selector, an input voltage from a plurality ofinput voltages, the plurality of the input voltages including at least atarget voltage and a preset reference voltage, the operation mode beingdetermined between a current measuring mode and a voltage measuring modein response to a control signal; and using the first plural switches,apply, as the selected input voltage, the preset reference voltage to aninput element in response to the operation mode being determined to bethe current measuring mode, and using the first plural switches, apply,as the selected input voltage, the target voltage to be measured to theinput element in response to the operation mode being determined to bethe voltage measuring mode; the input element connected to the inputvoltage selector and configured to convert the target voltage into acurrent in the voltage measuring mode, the current corresponding to thetarget voltage to be measured in the voltage measuring mode; an inputcurrent controller, including second plural switches, connected to theinput element and configured to control, using the second pluralswitches and the first plural switches, an inflow of an input current inconjunction with the determined operation mode of the input voltageselector, the second plural switches being different from the firstplural switches; and a measuring circuit, connected to output ends ofthe input element, configured to selectively measure one of the targetvoltage and the input current, dependent on the determined operationmode of the input voltage selector, using the first plural switches andthe second plural switches.
 2. The apparatus of claim 1, wherein thepreset reference voltage has a fixed voltage level or a variable voltagelevel.
 3. The apparatus of claim 1, wherein the measuring circuit,connected to the output ends of the input element and using the firstplural switches and the second plural switches, is further configuredto: measure the target voltage, selected as the input voltage, when thedetermined operation mode of the input voltage selector is the voltagemeasuring mode, and measure the input current when the determinedoperation mode of the input voltage selector is the current measuringmode.
 4. The apparatus of claim 3, wherein the input current controlleris configured to: allow the inflow of the input current into the signalprocessing apparatus in the current measuring mode by controlling, usingthe first plural switches and the second plural switches, respectiveswitching connections of the input current controller, and block theinflow of the input current in the voltage measuring mode bycontrolling, using the first plural switches and the second pluralswitches, the respective switching connections.
 5. The apparatus ofclaim 3, wherein the input current controller comprises an input currentcompensator configured to output a compensation current to adjust alevel of the input current in the current measuring mode.
 6. Theapparatus of claim 5, further comprising an input current compensationcontroller configured to control a level of the compensation currentoutput by the input current compensator based on an output signal of thesignal processing apparatus, wherein the output signal of the signalprocessing apparatus is a signal output through the input element. 7.The apparatus of claim 5, further comprising: a low-pass filterconnected to the input element and configured to extract a signal of alow-frequency band from an output signal of the signal processingapparatus and output the signal of the low-frequency band; a comparatorconnected to the low-pass filter and configured to compare a level ofthe signal output by the low-pass filter to a level of a presetreference signal and output a signal indicating a result of thecomparing; and an input current compensation controller, connected tothe comparator and the input current compensator, configured to generateanother control signal to control the input current compensator based onthe signal output by the comparator.
 8. The apparatus of claim 3,wherein the input current controller comprises a chopper configured tomodulate a frequency component of the input current based on anothercontrol signal in the current measuring mode.
 9. The apparatus of claim1, further comprising a load element functionally connected to the inputelement and the input current controller.
 10. The apparatus of claim 9,wherein an output end of the input current controller is connected toboth ends of the load element, and one end of the input element isconnected to one of the ends of the load element.
 11. The apparatus ofclaim 1, further comprising: a voltage receiving circuit configured toreceive an input voltage corresponding to a first measured biosignal;and a current receiving circuit configured to receive an input currentcorresponding to a second measured biosignal.
 12. A signal processingapparatus comprising: an input voltage selector, including first pluralswitches, configured to: select, using the first plural switches, apreset reference voltage, as an input voltage from a plurality of inputvoltages, in response to a current measuring mode being determined basedon a control signal, and select, using the first plural switches, atarget voltage to be measured, as the input voltage from the pluralityof input voltages, in response to a voltage measuring mode beingdetermined based on the control signal; apply, using the first pluralswitches, the preset reference voltage to an input element in responseto the determined current measuring mode, and apply, using the firstplural switches, the target voltage to the input element in response tothe determined voltage measuring mode; the input element connected tothe input voltage selector and configured to convert the applied targetvoltage into a current corresponding to the applied target voltage inresponse to the determined voltage measuring mode; an input currentcontroller, including second plural switches, connected to the inputelement and configured to control, using the second plural switches andthe first plural switches, an inflow of an input current in conjunctionwith a determined measuring mode of the input voltage selector, thesecond plural switches being different from the first plural switches; aload element functionally connected to the input element and the inputcurrent controller, wherein an output end of the input currentcontroller is connected to both ends of the load element, and one end ofthe input element is connected to one of the ends of the load element;and a measuring circuit, connected to output ends of the input element,configured to selectively measure one of the applied target voltage andthe input current, dependent on the determined operation mode of theinput voltage selector, using the first plural switches and the secondplural switches.
 13. The apparatus of claim 12, wherein the presetreference voltage has a fixed voltage level or a variable voltage level.14. The apparatus of claim 12, wherein the measuring circuit, connectedto the output ends of the input element and using the first pluralswitches and the second plural switches, is further configured to:measure the input voltage when the determined measuring mode of theinput voltage selector is the voltage measuring mode, and measure theinput current when the determined measuring mode of the input voltageselector is the current measuring mode.
 15. The apparatus of claim 14,wherein the input current controller is configured to: allow the inflowof the input current into the signal processing apparatus in the currentmeasuring mode by controlling, using the first plural switches and thesecond plural switches, respective switching connections of the inputcurrent controller, and block the inflow of the input current in thevoltage measuring mode by controlling, using the first plural switchesand the second plural switches, the respective switching connections.16. The apparatus of claim 14, wherein the input current controllercomprises an input current compensator configured to output acompensation current to adjust a level of the input current in thecurrent measuring mode.
 17. The apparatus of claim 16, furthercomprising an input current compensation controller configured tocontrol a level of the compensation current output by the input currentcompensator based on an output signal of the signal processingapparatus, wherein the output signal of the signal processing apparatusis a signal output through the input element.
 18. The apparatus of claim16, further comprising: a low-pass filter connected to the input elementand configured to extract a signal of a low-frequency band from anoutput signal of the signal processing apparatus and output the signalof the low-frequency band; a comparator connected to the low-pass filterand configured to compare a level of the signal output by the low-passfilter to a level of a preset reference signal and output a signalindicating a result of the comparing; and an input current compensationcontroller, connected to the comparator and the input currentcompensator, configured to generate another control signal to controlthe input current compensator based on the signal output by thecomparator.
 19. The apparatus of claim 14, wherein the input currentcontroller comprises a chopper configured to modulate a frequencycomponent of the input current based on another control signal in thecurrent measuring mode.
 20. The apparatus of claim 12, furthercomprising: a voltage receiving circuit configured to receive an inputvoltage corresponding to a first measured biosignal; and a currentreceiving circuit configured to receive an input current correspondingto a second measured biosignal.